The European Union's top court ordered Poland on Friday to immediately stop applying a law that lowered the retirement age for Supreme Court judges, forcing some 20 off the bench.

The interim injunction from the European Court of Justice also obliges EU member Poland to reinstate the judges who had to retire early after the law took effect in July. It lowered the age limit for Supreme Court service from 70 to 65.

The powerful leader of Poland's conservative ruling party, Jaroslaw Kaczynski, said Poland would observe EU law, but not whether the government would comply with the order. He also said the government would do all it could to "defend our state interest."

The European Commission, the EU's executive branch, asked for the injunction while the Court of Justice considers its challenge to the age cap as a violation of EU laws on judicial independence and the right to a fair trial. A ruling in the main proceedings is expected later.

Supreme Court judges, arguing the forced retirements are an infringement of Poland's Constitution, also have sought the European court's opinion.

Kaczynski's Law and Justice party has made overhauling the judicial system a key focus since it came to power in 2015. The government maintains that removing justices who were active during Poland's communist era will make the courts more efficient and fairer.

Among the evidence Court of Justice Vice President Rosario Silva de Lapuerta cited in the order was "a profound and immediate change in the composition of the Supreme Court" since the disputed law went into force. Along with the retirements, an increase in court seats from 93 to 120 created more than 44 vacancies, and President Andrzej Duda has filled at least 27 of them, Lapuerta said.